Angiogenesis or neovascularization is critical for normal physiological processes such as embryonic development and wound repair (Folkman and Shing, J. Biol. Chem. 1992, 267:10931-10934; D'Amore and Thompson, Ann. Rev. Physiol. 1987, 49:453-464). However, angiogenesis also occurs pathologically, for example, in ocular neovascularization (leading to diabetic retinopathy, neovascular glaucoma, retinal vein occlusion and blindness), in rheumatoid arthritis and in solid tumors (Folkman and Shing, J. Biol. Chem., 1992, 267:10931-10934; Blood and Zetter, Biochim. Biophys. Acta., 1990, 1032:118-128).
Tumor dissemination, or metastasis, involves several distinct and complementary components, including the penetration and traversing of tumor cells through basement membranes and the establishment of self-sustaining tumor foci in diverse organ systems. To this end, angiogenesis is critical to tumor survival. Without neovascularization, tumor cells lack the nourishment to divide and will not be able to leave the primary tumor site (Folkman and Shing, J. Biol. Chem., 1992, 267:10931-10934).
Inhibition of angiogenesis in animal models of cancer has been shown to result in tumor growth suppression and prevention of metastatic growth (Herblin et al., Exp. Opin. Ther. Patents, 1994, 1-14). Many angiogenic inhibitors have been directed toward blocking initial cytokine-dependent induction of new vessel growth, e.g. antibodies to endothelial cell growth factors. However, these approaches are problematic because tumor and inflammatory cells can secrete multiple activators of angiogenesis (Brooks et al., Cell, 1994, 79:1157-1164). Therefore, a more general approach that would allow inhibition of angiogenesis due to a variety of stimuli would be of benefit.
The integrin .alpha..sub.v.beta..sub.3, sometimes called the vitronectin receptor, is preferentially expressed on angiogenic blood vessels in chick and man (Brooks et al., Science, 1994, 264:569-571; Enenstein and Kramer, J. Invest. Dermatol., 1994, 103:381-386). .alpha..sub.v.beta..sub.3 is the most promiscuous member of the integrin family, allowing endothelial cells to interact with a wide variety of extracellular matrix components (Hynes, Cell, 1992, 69:11-25). These adhesive interactions are considered to be critical for angiogenesis since vascular cells must ultimately be capable of invading virtually all tissues.
While integrin .alpha..sub.v.beta..sub.3 promotes adhesive events important for angiogenesis, this receptor also transmits signals from the extracellular environment to the intracellular compartment (Leavesley et al., J. Cell Biol., 1993, 121:163-170, 1993). For example, the interaction between the .alpha..sub.v.beta..sub.3 integrin and extracellular matrix components promotes a calcium signal required for cell motility.
During endothelium injury, the basement membrane zones of blood vessels express several adhesive proteins, including but not limited to von Willebrand factor, fibronectin, and fibrin. Additionally, several members of the integrin family of adhesion receptors are expressed on the surface of endothelial, smooth muscle and on other circulating cells. Among these integrins is .alpha..sub.v.beta..sub.3, the endothelial cell, fibroblast, and smooth muscle cell receptor for adhesive proteins including von Willebrand factor, fibrinogen (fibrin), vitronectin, thrombospondin, and osteopontin. These integrins initiate a calcium-dependent signaling pathway that can lead to endothelial cell and smooth muscle cell migration and, therefore, may play a fundamental role in vascular cell biology.
Recently, an antibody to the .alpha..sub.v.beta..sub.3 integrin has been developed that inhibits the interaction of this integrin with agonists such as vitronectin (Brooks et al., Science, 1994, 264:569-571). Application of this antibody has been shown to disrupt ongoing angiogenesis on the chick chorioallantoic membrane (CAM), leading to rapid regression of histologically distinct human tumor transplanted onto the CAM (Brooks et al., Cell, 1994, 79:1157-1164). In this model, antagonists of the .alpha..sub.v.beta..sub.3 integrin induced apoptosis of the proliferating angiogenic vascular cells, leaving pre-existing quiescent blood vessels unaffected. Thus, .alpha..sub.v.beta..sub.3 integrin antagonists have been shown to inhibit angiogenesis and are recognized as being useful as therapeutic agents for the treatment of human diseases such as cancer, restenosis, thromoembolic disorders, rheumatoid arthritis and ocular vasculopathies (Folkman and Shing, J. Biol. Chem., 1992, 267:10931-10934).
Increasing numbers of other cell surface receptors have been identified which bind to extracellular matrix ligands or other cell adhesion ligands thereby mediating cell-cell and cell-matrix adhesion processes. Like the .alpha..sub.v.beta..sub.3 integrin, these receptors belong to the integrin gene superfamily and are composed of heterodimeric transmembrane glycoproteins containing .alpha.- and .beta.-subunits. Integrin subfamilies contain a common .beta.-subunit combined with different .alpha.-subunits to form adhesion receptors with unique specificity. The genes for eight distinct .beta.-subunits have been cloned and sequenced to date.
The integrin .alpha..sub.v.beta..sub.3 is a member of the .beta..sub.3 integrin subfamily and has been described on platelets, endothelial cells, melanoma, smooth muscle cells, and osteoclasts (Horton and Davies, J. Bone Min. Res. 1989, 4:803-808; Davies et al., J. Cell. Biol. 1989, 109:1817-1826; Horton, Int. J. Exp. Pathol., 1990, 71:741-759). Like the major platelet integrin GPIIb/IIIa, the vitronectin receptor binds a variety of RGD-containing adhesive proteins such as vitronectin, fibronectin, von Willibrand factor, fibrinogen, osteopontin, bone sialoprotein II and thrombospondin in a manner mediated by the RGD sequence.
A key event in bone resorption is the adhesion of osteoclasts to the matrix of bone. Studies with monoclonal antibodies have implicated the .alpha..sub.v.beta..sub.3 receptor in this process and suggest that a selective .alpha..sub.v.beta..sub.3 antagonist would have utility in blocking bone resorption in diseases such as osteoporosis (Horton et al., J. Bone Miner. Res., 1993, 8:239-247; Helfrich et al., J. Bone Miner. Res., 1992, 7:335-343).
The use of iontophoresis, also referred to as electrotransport, in drug delivery is well known. Controlled, continuous delivery of drugs at constant rates is a highly useful method of delivering medications. This kind of delivery ensures relatively constant plasma concentrations and, more importantly, proper control of pharmacologic and toxic drug effect. Transdermal delivery can be an especially useful means of controlled, continuous delivery of drugs that exhibit no/low oral bioavailability while avoiding the inconvenience and discomfort of administration by injection. However, most drugs do not diffuse through the skin at rates sufficient for delivering therapeutic doses. Skin is specially impermeable to polar and ionic drugs. The transdermal administration of drugs for which the skin is normally impermeable requires utilizing techniques for enhancing the skin permeation of the drug. One of these techniques is iontophoresis. In order to deliver molecules across the skin in adequate quantity, it must have a net charge. However, we found that sometimes even if the molecule has a net charge, it cannot be delivered effectively iontophoretically due to other physical chemical characteristics, such as surface activity and relatively high partition coefficient which can result in low delivery rate. This invention is related to the iontophoretic delivery of .alpha..sub.v.beta..sub.3 antagonists through special prodrugs that provide relatively high delivery rates.
.alpha..sub.v.beta..sub.3 receptor antagonists typically have very low/no oral bioavailability and short plasma half-life which make them poor candidates for oral delivery. Controlled delivery systems that administer these compounds or suitable prodrugs of these compounds at constant rate can produce plasma concentrations that would be maintained in the desired range.
This invention relates to novel methods and devices for iontophoretically administering therapeutic doses of integrin receptor antagonists in a controlled manner through the skin. Alkyl esters of the .alpha..sub.v.beta..sub.3 integrin inhibitors cannot be delivered efficiently through transdermal iontophoresis because they exhibit high surface activity and self-association. Prodrugs that carry an amine or ammonium functional group on the promoiety provide minimal self-association and high transdermal iontophoretic flux.